Pull Fault codes on '89 100? Out of luck?

Hello esteemed list:
I am trying to diagnose and fix a intermittent low idle problem. Car has
122,000mi on it and about 75% of the time Idles at about 600rpm with the A/C
off. When A/C comes on it drops down to about 400.
I have access to a bentley for the '88 5000 which goes into detail on how to
pull and read the codes for the CIS-III cars but when I try to follow the
procedure (engine running, fuse into Fuel Pump relay for 4 seconds, remove)
I don't get any flashing light. None, Nada. The owners manual seems to
indicate that the "Check engine" light might have only been put on
California models. Is there another way I can read the fault codes?
Anyone have any ideas about the idle problem? I'm leaning towards the Idle
switch or wiring to it being bad. When it idles correctly at about 750, the
a/c is correctly compensated for, i.e. the idle stays at about 750.
Any help would be appreciated.
Thanks,
Jeff